Automatic synchronizer



15, 1934. F. H. GULLIKSEN AUTOMATIC SYNCHRONIZER Filed Juhe so INVENTOR/?7m//. Gull/K6120.

AT'i'ORNEY fF'eQuen cg D/X/erance WITNESSES I- Patented Oct. 16, 1934 mmAUTOMATIC SYNCHRONIZEB Finn ll. Gnllihen, Wllkinsburg, 2a., alsignor toWestinghouse Electric It Manufacturing Company, a corporation ofPennsylvania Application June 30, 1931, Serial No. 547,895

"Claims.

My invention relates, in general, to automatic 'synchronizers and moreparticularly to automatic synchronizers of the thermionimtube type,designed to control the paralleling of two alternatlug-current sources,under predetermined conditions.

Various designs of automatic synchronizers, of

l the mechanical type, have been built according to the teachings of theprior art and are now being extensively utilized in generating stationsand sub-stations to improve the paralleling service and to relieve theoperators in these stations of the responsibility involved inparalleling large ,power systems.

However, automatic synchronizers of the mechanical type are complicatedin construction and require expensive and elaborate calibration andadjustment. Because of the friction and inertia of the moving parts of amechanical synchronizer 29 a relatively large amount oi energy isrequired to operate them, which imposes a high volt-ampere burden uponthe instrument transformers which connect the synchronizer to the powersystems. Mechanical synchronizers, therefore, cannot be operated fromstandard condenser bushing potential devices, which have a relativelylow voltampere capacity.

An object of my invention, generally stated, is to provide an automaticsynchronizer, of the thermionic-tube type, which shall be simple andeilicient in operation, and which may be readily and economicallymanufactured and installed.

A more speciflc'object of my invention is to provide for initiating theclosing of a switch for 5 paralleling two alternating-current sources atan advanced phase angle, proportional to the instantaneous frequencydifference between the current sources, to permit the current sources tobe paralleled at substantially zero phase-angle 0 displacement.

, Another object of my invention is to prevent fully-hereinafter, orwill be apparent to those skilled in the art.

Inaccordance with my invention, a switch for paralleling twoalternating-current sources is controlled by relays which are energizedby electronic tubes connected to the current sources.

' f the closing of a switch for paralleling two alter- The relays aresointerlocked that the paralleling of the two sources is effected onlywhen the phase and frequency relations are suitable.

For a fuller understanding of the nature and scope of my invention,reference may be had to the following detailed description, taken inconjunction with the accompanying drawing, in which:

Figure l is a diagrammatic view of an automatic synchronizer embodyingmy invention, together with the circuits necessary for a properfunctioning thereof and Fig. 2 is a graphical representationillustrating the operating characteristics of the automatic synchronizershown in Fig. 1.

Referring to the drawing, the reference character 10 designates aparalleling switch that is disposed to parallel two sources ofalternating current (not shown) which are cormected to the two groups ofpower conductors designated byreference characters 11 and 12. The switch10 may be ofa standard type having a closing solenoid mechanism 13 and atripping mechanism 14.

As shown, the energization of the closing solenoid 13 is controlled byan automatic synchronizer, which will be described in detailhereinafter, and the tripping mechanism 14 may be controlled by a masterrelay 15. The operation of the relay 15 may be controlled by apush-button switch 16, which establishes an energizing circuit foractuating coil of the relay 15, and a second pushbutton switch 17, whichinterrupts the circuit for the actuating coil. A holding circuit isestablished by means of a contact member 18, on the relay 15, after therelay is actuated to the closed position. When the relay 15 is in theopen or deenergized position, the tripping mechanism 14 is energized bymeans of a contact member 19 on the relay 15. An auxiliary relay 21 isprovided for disconnecting the synchronizing apparatus from the powersources after the paralleling switch 10 s As illustrated, the thermionicsynchronizer comprises two standard vacuum tubes 22 and 23, of the threeelectrode type, which are" connected in series with their respectiverelays 22' and 23'.

The synchronizer is connected to the two power systems 11 and 12 bymeans including transformers 24 and 25, each of which comprises aprimary winding and three secondary windings. The primary windings ofthe transformers 24 and 25 are connected to potential transformers 26and 27, respectively, through contact members of the relays 15 and 21.The potential transformers 26 and 27 are energized from the respectivepower systems 12 and 11, which are to be paralleled.

The secondary windings 28 and 29 of the transformers 24 and 25, are soconnected to the alternating-current terminals of a rectifier 31, whichis preferably of the well-known copper oxide type comprising aWheatstone bridge arrangement of copper oxide'discs, that the voltagesof the two systems are directly opposed when the phase angledisplacement between the systems is zero,

thereby applying a beat voltage to the rectifierproportional tothefrequency difference between the systems. .The direct-current 'v-oltageout: put of the rectifier 31 is therefore essentially a pulsatingvoltage which varies according to a composite sine wave between zero andmaximum, once per second for each cycle frequency difference between thetwo systems to be paralleled. It will be understood that the voltageimpressed on the rectifier is a maximumand consequently the outputvoltage is highest, when the phase angle displacement between the systemvoltages is 180 degrees. A condenser 32 is connected across thedirect-current terminals of the rectifier 31 to smooth out thealternating-current components of the rectified voltage. Resistors 66and 67 and a condenser 68 are also connected across the terminals of therectifier 31. These are utilized to apply. a grid bias to the tube 22,as will be explained in detail hereinafter.

Another multiple rectifier 33 is connected to the secondary windings 34and 35, of the transformers 24 and 25, in the same manner as therectifier 31. A condenser 36 and'a resistor 59 are also connected acrossthe direct-current terminals of the rectifier. Accordingly, the outputvoltage of the rectifier '33 also varies from zero to maximum, once persecond for each cycle frequency difference between the 'two systems.

In addition to the foregoing apparatus, a breaker closing relay3'7 andan intermediate relay 38 are provided. One set of contact members oftherelay 37 controls the energization of the closing solenoid 13, andthe other set is utilized to establish a holding circuit for the relay.The

' energization of the actuating coil of the relay 37 is controlled bythe relays .22 and 23'. The function of relay 38 is to interpose a timedelay, corresponding to on phase rotation, .when the synchronizer isfirst given control thereby ensuring that synchronizing will nottalreplace any reliablesource of direct-current energy. As

previously explained, the synchronizing appa-' ratus is automaticallydisconnected from both the alternating .and the direct-current sourcesof energy when the circuittbreaker 10 is closed,

in order that the life of the apparatus will be increased.

As previously stated, there are two require-- ments which should befulfilled by an automatic synchronizer: first, the synchronizer shouldoperate to energize the paralleling-switch closing solenoid only if theinstantaneous frequency difference between the two systems to beparalleled is less than a predetermined lock-out frequency difference,in order to prevent tying together generators which are operating at toogreat a difierence in speed. Secondly, the paralleling switch closingmechanism should be energized at an advance phase angle proportional tothe instantaneous frequency difference, to make allowance for the timerequired for relay operation and circuit breaker closing, in order.thatthe two systems will be paralleled at substantially the exact instant ofzero phase angle displacement between the voltages of the two systems.

It will be evident from the following description of operation that theautomatic synchronizer, herein disclosed, meets the foregoingrequirements. the paralleling switch 10 under the control of theautomatic synchronizer, the push-button switch 16 may be closed toenergize the actuating coil of the relay 15, from the direct-currentsupply circuit 39, thereby causing the relay to be actuated to itsuppermost position. When the'relay 15 is actuated, the conductors 41 and42 are connected to the direct-current control bus 39, and the primarywindings of the transformers 24 and 25 are energized from the potentialtransformers 26 and 2'1, respectively, provided relay 21 remains in itsnormal or lower position.

The thermionic tube 23 is adapted to be con- Assuming that it is desiredto put nected in series with the actuating coil of relay 23 across thedirect-current conductors 41 and 42. It will be seen that the filament43 of the tube 23 is supplied with heating current by the secondarywinding 44 of the transformer 25, also that the filament 45 of the tube22 is heated by the secondary winding 46 of the transformer 24. Mid-tapconnections are provided to the windings 44 and 46, as shown on thedrawing, for a purpose to be set forth below. The energizing circuit forthe actuating coil of the relay 23', which is established through thetube 23 provided the contact members of the relay 38 are closed, as willbe explained hereinafter, extends from the positive conductor 41,through conductor 47, the contact members 48 of the relay 22' in itslower position, conductors 49 and 51, the contact members 52 of therelay 38 in its upper position, conductor 53, the coil of the relay 23',conductor 54, the plate 55 of the tube 23, the filament 43, thence tothe mid-tap conductor 56 and a portion of the potentiometer resistor5'7, to the negative conductor 42.

By means of the potentiometer 57, the grid 58 of the tube 23 is suppliedwith a negative bias which may be varied by changing the potentiometersetting. In addition to this-bias, a negative bias equal to one half thevoltage across the rectifier 33 is also applied to the grid 58.

degrees. Therefore, the negative bias applied to the grid 58 is also amaximum when the system voltages are 180 degrees out of phase. When thephase angle is reduced, the negative bias on grid 58 is reduced until apoint is reached where the total negative bias on the grid is low enoughto permit suflicient current to how through the tube to operate relay23', thereby closing its contact members. The phase angle displacementat which the relay 23' is permitted to operate may be varied byadjusting the potentiometer 57. The relay 23' will, therefore, operateand.

close its contacts at a fixed point in advance of synchronism, theclosing characteristic being independent of the frequency difierencebetween the two systems, as illustrated by curve b of i 2. I

As shown, the actuating coil of the relay 22' is connected in serieswith the thermionic tube 22, through a circuit which extends from thepositive conductor 41, through conductor 47, the coil of relay 22',conductor 62, the plate 63, the filament 45, thence to the mid-tapconductor 64, and a portion of the potentiometer resistor 65, to thenegative conductor 42. Accordingly, the operation of the relay 22' iscontrolled by the tube 22 ,in somewhat the same manner as the tube 23controls the relay 23.

However, the relay 22' will operate and close it contacts at a point inadvance of synchronism proportional to the frequency difierence, asillustrated by curve "a of Fig. 2. The proportional advancecharacteristic of relay 22 is produced by the combined action of therectifier 31, resistors 66 and 67, and the condenser 68.

I As previously explained, the direct-current output voltage ofthe-rectifier 31 pulsates at a rate proportional to the frequencydiilerence between the two systems to be paralleled. The voltage acrossthe condenser 68, when the frequency difference is zero, is equal to theoutput voltage of the rectifier 31. If there is a definite frequencydifference between the two systems and the phase angle displacement ischanging from 180 degrees towards zero, then the voltage across theterminals of the rectifier 31 and the voltage across the condenser 68will be decreasing, but the voltage across the condenser 68 will behigher than the rectifier voltage by an amount dependent upon thefrequency difference. The discharge current from the condenser, whichflows in the direction indicated by the arrow 69, will produce a voltagedrop across the resistor 67 with polarity as indicated. When the phaseangle displacement between the system voltages is increasing from zeroto 180 degrees the polarity of the voltage drop across the resistor willbe reversed. The magnitude of the voltage drop across the resistor 67 isproportional to the frequency difference.

The resistor 67 is so connected in the grid circuit of the tube 22 thatthe voltage drop across the resistor will give a positive bias to thegrid 71 when the phase angle displacement is decreasing from 180 degreestoward zero and the condenser 68 is discharging through the resistor 67.

A A constant negative bias is'applied to the grid 71 by means of thepotentiometer 65 and a varying negative bias, which is proportional tothe phase angle displacement, is obtained from the rectifier 33. Thegrid circuit for the tube 22 may be traced from the potentiometer 65,through the mid-tap conductor 64, the filament 45, the grid 71,conductor 72, the resistor 67, conductor 73, the rectimi- 33, andconductors 74 and 61. to the negative conductor 42.

The potentiometer 65 is so adjusted that the negative grid bias obtainedfrom the potentioometer is just low enough to permit sufiicient currentto flow through the tube 22 to operate the relay 22' at zero phase angledisplacement when the frequency diiference between the two systems iszero. For any definite frequency difference, a definite positive bias isapplied to the grid of tube 22 which will reduce the total negative biason the grid, and relay 22' will therefore operate at an advanced phaseangle position, the amount of advance being proportional to theinstantaneous frequency difference. The operating characteristics ofrelay 22' are illustrated by curve a of Fig. 2.

As shown in Fig. 2, the relay 23 will operate and close its contactmembers at a fixed point in advance of synchronism, the closingcharacteristic being independent of the frequency difference, asillustrated by line b, while the relay 22' will close its contactmembers at a pointin advance of synchronism proportional to thefrequency difierence, according to line a of Fig. 2. Therefore, it willbe seen that if the frequency diiference is less than the valuerepresented by ",f, the point of intersection of curves a and b, therelay 23' will operate at a larger phase angle displacement than therelay 22', but if the frequency difference is above the value of f therelay 22' will operate at a larger phase angle than the relay 23.

As shown in Fig. 1, the contact members of the relays 22 and 23' are sointerlocked that the breaker closing relay 37 is energized only if therelay 23' is operated before the relay 22 is closed. It will be seenthat both of the relays 22' and 23' must be closed before the relay 37can operate because the actuating coil of the relay 37 is connected inseries with the normally open contact members of the relays 22 and 23.The relay 23' must operate ahead of the relay 22', since the energizingcircuit for the actuating coil of the relay 23 extends'through thenormally closed contact member 48, of the relay 22, as was previouslyergizing the breaker closing coil at an advanced 7.

phase angle proportional to the instantaneous frequency difference. Theamount of advance at which the relay 22' will operate, may be varied byadjusting the potentiometer 66 to provide for the time required to closethe particular breaker being controlled, thereby causing the breaker tobe closed at substantially exactly zero phase angle displacement.

In addition to the relays 22' and 23, and the breaker closing relay37,an intermediate relay 38 is also provided. The function of this relayis to interpose a time delay corresponding to one phase rotation whenthe synchronizer is first given control of the circuit breaker 10, aswill be explained hereinafter, and thus prevent synchronizing until thecondenser 68 has assumed the charge corresponding to the instantaneousphase angle displacement and frequency difierence.

When the synchronizer is given control by actuating the push-buttonswitch 16 to energize the master relay 15, the, sequence of relayoperation is as follows: The relay 22' is actuated t its uppermostposition the first time that the phase angle displacement between thesystem voltages the relay 3'7 to operate.

established through the actuating coil of the relay 38, which extendsfrom the positive conductor 41, through conductor 4'7, the bridgingcontact members '75 of relay 22, conductor '76, the coil of the relay38, and a resistor 7'7, to the negative conductor 42.

When the contact members of the relay 38 are closed a holding circuit isestablished which keeps the coil 38 energized after the relay 22' hasdropped to its lowermost position. The holding circuit may be tracedfrom the positive conductor 41, through conductors 4'7 and '78, thebridging contact members 79 and the coil of the relay 38, and resistor'77, to'the negative conductor 42.

If the frequency difference, when the phase angle during the next beatis decreasing from 180 degrees towards zero, is higher than the selectedlockout frequency difference, the relay 22' will again operate at apoint in advance of synchronism and close its contact members before therelay 23' operates. Since the normally closed contact members 48 of therelay 22' are connected in series with the actuating coil of relay 23',the relay 23' cannot operate until the relay 22', drops to its lowermostposition at zero phase angle displacement. Therefore, synchronizing willnot take place if the frequency difference is higher than the selectedlockout frequency.

However, when the frequency difference between the two systems becomesless than the selected lockout frequency difference, the relay 23' willoperate ahead of the relay 22', as previously explained. When the relay22 finally operates at the proper phase advance,relay 23 will, becauseof the action of 'a. condenser 81 connected across the coil of relay 23,remain closed for a time interval of sufiicient length to permit Thecircuit for the actuating coil of relay 3'7 may be traced from thepositive conductor 41, through conductor 4'7, the bridging contactmembers 82 of the relay 22', conductor 83, the bridging contact members84 of the relay 23, conductor 85, the coil of the relay 3'7, andconductor 86, to the negative conductor 42.

A holding circuit for the actuating coil of relay 3'7 is establishedwhen its contact members are closed. The holding circuit may be tracedfrom the positive conductor 41, through conductor 87, bridging contactmembers 88 and the coilof the relay 3'7, and conductor 86, to thenegative conductor 42.

When'the relay 3'7 is operated, an energizing circuit is established forthe actuating coil of the breaker closing mechanism 13, thereby closingtheparalleling switch 10 and completing the synchronizing operation. Thecircuit for the coil of the closing mechanism may be traced from thepositive conductor 41, through bridging contact members 89 of the relay3'7, conductor 91, the

.actuating coil of the closing mechanism 13- and conductor 92, to thenegative conductor 42.

It will be observed that the actuating coil of the relay 21 isenergizediby means of an interlock 20 on the circuit breaker 10 when thecircuitbreaker is closed. Accordingly, the relay 21 is actuated to itsupper position and the conductor '42 is disconnected from the controlbus 39. The

potential transformers 26 and 27 are also disconnected from thetransformers 24 and 25 when the relay 21 is operated. In this manner,the automatic synchronizer is dee'nergized while the two systems areparalleled which, as previously exis zero. When the relay 22 operates, acircuit is plained, greatly increases the life of the thermionic tubes22 and 23.

Since the paralleling switch 10 cannot be closed unless both of therelays 22' and 23' are operated, the synchronizer is made inoperative bythe failure'of one of the tubes 22 or 23. In this manner, the twosystems-are prevented from being paralleled unless the previouslymentioned pre-requisite conditions are fulfilled. Therefore, faultysynchronizing because of tube failure is prevented.

When the synchronizer is utilized for controlling a paralleling switchwhich may be the last switch to be closed in a loop or ring powersystem, there will be nophase rotation between the voltages of the powerconductors which are to be paralleled although there may be a phaseangle displacement. Under these conditions, the relays 22' and 23' wouldnot operate in the proper sequence, as previously explained, to effectthe closing of the paralleling switch.

In order that the synchronizer may be utilized in a loop system,.theactuating coil of a voltage relay 93 of the well-known revolving .disctype, having a time delay action, is connected through conductors 97 and98 to the primary windings of the transformers 24 and 25, which in turnare connected across the potential transformers 26 and 27, as shown inthe drawing. The contact members 94 and 95, which are disposed to bebridged by a contact member 96 of the relay 93, are connected inparallel-circuit relation to the normally closed contact members 48 ofthe relay 22'. Therefore, when the relay 93 actuates the contact member96 to bridge the contact members 94 and 95, the relay 23' may operateafter the relay 22' to effect the closing of the paralleling switch 10.However, the time delay feature of the relay 93 may be so adjusted thatthe relay has no eife'ct when the synchronizer is utilized to controlthe paralleling switches of power systems of the usual type.

It will be evident from the foregoing description that I have providedan automatic'synchronizer which will effect the operation of aparalleling switch to connect two power systems at substantially theexact instant of zero phase angle displacement between the voltages ofthe two systems, provided the frequency difference between the twosystems to be paralleled is less than a predetermined value.

It will also be evident that the automatic synchronizer herein describedhas the following advantages over synchronizers of previously knowntypes:

(a) Low power consumption.

(b) No friction between moving mechanical parts.

(c) May be readily adjusted, when installed, to meet difierent operatingconditions. a

(d) Inexpensive in construction and efilcient and reliable in operation.

In conclusion, I desire to say that I am not to be restricted to thespecific embodiment of my invention herein shown and described, since it.is evident that it may be changed or modified without departing fromthe spirit and scope of my invention as defined in the appended claims.

I claim as my invention:

1. In a system for paralleling alternating-cur-- rent sources, thecombination of a paralleling switch, switching means for controlling the0105- ing of said paralleling switch, and means for effecting theoperation of said switching means at an advanced phase angleproportional to the frequency difference between the two current sourcescomprising means for controlling the switching means and an electronictube responsive to control potentials proportional to the intheoperation of said switching means at an ad vanced phase angleproportional to the frequency difierence between the two current sourcescomprising a relay for controlling the switching means and an electronictube responsive to control potentials proportional to the instantaneousfrequency diilerence between the current sources for controlling theenergization of said relay, and means for varying the advanced angle atwhich said relay is energized.

3. In a system for paralleling alternating-current sources atsubstantially the instant of phase coincidence, the combination of aparalleling switch, switching means for controlling the operation 015said paralleling switch, electronic tube means responsive to controlpotentials proportional to the phase angle displacement between thevoltages of the sources for controlling said switching means, electronictube means responsive to control potentials proportional to thefrequency diflerence between the current sources for effecting theoperation of said switching means at a phase displacement in advance ofphase coincidence proportional to the frequency diilerence, and meansdisposed to prevent said switching means from closing the parallelingswitch so long as the frequency diilerence between the current sourcesto be paralleled is above a predetermined value.

4. In a system for paralleling altematingcurrent sources atsubstantially the instant of phase coincidence, the combination of aparalleling switch, switching means for controlling the operation ofsaid paralleling switch, electronic tube means responsive to controlpotentials proportional to the phase angle displacement between thevoltages of the sources for controlling said switching means, electronictube means responsive to control potentials proportional to thefrequency difference between the current sources for effecting theoperation of said switching means at a phase displacement in advance ofphase coincidence proportional to the frequency diiference, relay meansdisposed to prevent said switching means from closing the parallelingswitch so long as the frequency dinerence between the current sources tobe paralleled is above a predetermined value, and means for varying thefrequency diil'erence at which the paralleling switch may be operated.

5. Ina system for paralleling altematingcurrent sources at substantiallythe instant of phase coincidence, the combination of a parallelingswitch, switching means for controlling the operation of saidparalleling switch, means responsive to the phase angle displacementbetween the voltages of the sources for controlling said switching meanscomprising a relay and an electronic tube for controlling theenergization of the-relay, andmeans responsive to the frequencydiiference between the current sources for eflecting the operation ofsaid switching means at a phase displacement in advance of phasecoincidence proportional to the frequency diflerence comprising a relayand an electronic tube for controlling said relay, means forinterconnecting the contact members of said relays to control theoperation oi said switching means to prevent the closing of theparalleling switch so long as the frequency difference between thecurrent sources to be paralleled is above a predetermined value.

6. In a system for paralleling alternatingcurrent sources atsubstantially the instant of phase coincidence, the combination of aparalleling switch, switching means for controlling the operation ofsaid paralleling switch, means responsive to the phase angledisplacement between the voltages of the sources for controlling saidswitching means comprising a relay ,and an electronic tube forcontrolling the energization of the relay, means responsive to thefrequency diiIerence between the current sources for effecting theoperation of said switching means at a phase displacement in advance ofphase coincidence proportional to the frequency difierence comprising arelay andan electronic tube for controlling said relay, means forinterconnecting the contact members of said relays to control theoperation of said switching means to prevent the closing of theparalleling switch so long as the frequency difierence between thecurrent sources to be paralleled is above a predetermined value, andmeans for varying the frequency difierence at which the parallelingswitch may be operated. I. In a system for parallelingalternatingcurrent sources, the combination of a paralleling switch,switching means for controlling the closing of said paralleling switch,relay means actuated in accordance with the frequency difference betweensaid sources for energizing said switching means when the frequencydifference between the sources to be paralleled is below a predeterminedvalue and at a time in advance of the occurrence of zero phasedifference between said sources which is proportional to the frequencydifference, electronic tube means for controlling the energization ofsaid relay means, and means for deferring the energization of saidswltching'means after the first occurrence of zero phase difierence at afrequency difference below said predetermined value for a time intervalsubstantially'corresponding to one phase rotation of the voltages of thecurrent sources.

8. In a system for paralleling alternatingcurrent sources, thecombination of a paralleling switch, switching means for controlling theclosing of said paralleling switch, relay means actuated in accordancewith the frequency difierence between said sources for energizing saidswitching means when the frequency difl'erence between the sources to beparalleled is below apredetermined value and at a time in advance of theoccurrence of zero phase difference between said sources which isproportional to the frequency diiference, electronic tube means forcontrolling the energization of said relay means, means for deferringthe energization of said switching means after the first occurrence ofzero phase difference at a frequency difl'erence below saidpredetermined value for a time interval substantially corresponding toone phase rotation of the voltages of the current sources, and means forvarying the value of frequency diiference and the time in advance of theoccurrence of zero phase diiference between the sources at which saidswitching means may be energized.

9. A system for paralleling alternating-current sources including aparalleling switch, switching 15o means for controlling the closing ofsaid switch, and means for effecting the operation of said switchingmeans at a time, in advance of the occurrence of exact phase coincidenceproportional to the frequency difference between the sources to beparalleled when the frequency difference is below a predetermined value,comprising av plurality of relays and a plurality of electronic tubesresponsive to potentials proportional to the frequency differencebetween the current sources for controlling the operation of saidrelays.

10. A system for paralleling alternating-current sources including aparalleling switch, switching means for controlling the closing of saidswitch, means for effecting the operation of said switching means at atime in advance of the occurrence of exact phase coincidenceproportional to the frequency difference between the sources to beparalleled when the frequency difference is below a predetermined value,comprising a plurality of relays and a plurality of electronic tubesresponsive to potentials proportional to the frequency differencebetween the current sources for controlling the operation of saidrelays, means for applying a biasing potential to said electronic tubes,and means for varying the biasing potential to vary the value offrequency difference and the advanced phase angle at which saidswitching means may be operated.

11. An automatic synchronizer for paralleling altemating-current sourcescomprising a relay disposed to operate at a definite point in advance ofsynchronism, a second relay disposed to operate at an advanced phaseangle displacement proportional to the frequency difference between thesources to be paralleled, and electronic tubes disposed to be energizedby the beat voltage between the sources and responsive to potentialsproportional to the frequency difference between the current sources forcontrollingthe relays, the contact members of said relays being soconnected as to effect the paralleling of the sources only underpredetermined'conditions.

12. An automatic synchronizer for paralleling alternating-currentsources comprising a relay disposed to operate at a definite point inadvance of synchronism, a second relay disposed to operate at anadvanced phase angle displacement proportional to the frequencydifference between the sources to be paralleled, the contact members ofsaid. relays being so connected as to effect the paralleling of thesources only under predetermined conditions, electronic tubes disposedto be energized by the beat voltage between the sources and responsiveto potentials proportional to the frequency difference between thesources for controlling the relays, means for applying a biasing.

potential to the electronic tubes, and means for varying the biasinpotential, whereby the paralleling conditions may be varied.

13. In a system for paralleling .altematingcurrent sources, thecombination of a paralleling switch, and means for initiating theclosing of said switch at an advanced phase angle proportional to thefrequency difference between the current sources comprising anelectronic tube responsive to control potentials proportional to theinstantaneous frequency difference between the current sources forcontrolling the closing of the paralleling switch.

14. In a system for paralleling alternating-current sources, the.combination of a paralleling switch, means for closing said switch, andmeans for effecting the energization of 'said closing means at anadvanced phase angle proportional to the frequency difference betweenthe two current sources comprising an electronic tube responsive tocontrol potentials-proportional to the instantaneous frequencydifference between the current sources for controlling the energizationof the means for closing the paralleling switch.

15. In a system for paralleling alternating-current sources, thecombination of a paralleling switch, means for closing said switch,means for effecting the energization of the closing means at an advancedphase angle proportional to the frequency difference between the. twocurrent sources comprising a relay for controlling the 7 operation .ofthe means for closing the switch and an electronic tube-responsive tocontrol potentials proportional to the instantaneous frequencydifference between the current sources for controlling the energizationof said relay, and means for varying the advanced angle at which saidrelay is energized.

16. In a system for controlling the operation of a switch forparalleling alternating-current sources, in combination, relay means forcontrolling .the closing of said paralleling switch,

and means for effecting the operation of said relay means at an advancedphase angle proportional to the frequency difference between the currentsources comprising means for obtaining a potential proportional to thefrequency diifer-' ence between the current sources and an electronictube responsive to said potential forcontrolling the operation of saidrelay means.

. 17. In a system for controlling the operation of a switch forparalleling alternating-current sources, in combination, relay means forcontrolling the closing of said paralleling switch, and means foreffecting the operation. of said relay means at an advanced phase angleproportional to the frequency difference between the current sourcescomprising means for obtaining a potential proportional to the frequencydifference between the current sources, means for measuring the rate ofchange of potential and an electronic tube responsive to said potentialfor controllin the operation of said relay means.

18. In a system for controlling the operation of a switch forparalleling alternating-current sources, in combination, relay means forcontrol ling the closing of said paralleling switch, and means foreffecting the operation of said relay means at an advanced phase angleproportional to the frequency difference between the current sourcescomprising means for obtaining a rectifled potential proportional to thefrequency difference between the current sources, means for measuringthe rate of change of said potential and an electronic tube responsiveto said potential for controlling the operation of said relay means.

FINN H. GULLIKSEN.

